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Re: [CSS2.1] Clarifying 8.3.1 Collapsing Margins

From: Anton Prowse <prowse@moonhenge.net>
Date: Fri, 20 Aug 2010 20:28:23 +0200
Message-ID: <4C6EC947.4040401@moonhenge.net>
To: "www-style@w3.org" <www-style@w3.org>
CC: fantasai <fantasai.lists@inkedblade.net>
On 19/08/2010 20:36, fantasai wrote:
> This is for CSS2.1 Issue 159
>   http://wiki.csswg.org/spec/css2.1#issue-159
> triggered by this email
>   http://lists.w3.org/Archives/Public/www-style/2010Feb/0015.html
> This is version 3.

>  | Adjoining vertical margins collapse, except:
>  |   * If the top and bottom margins of an element with clearance are
>  |     adjoining, its margins collapse with the adjoining margins of
>  |     following siblings but that resulting margin does not collapse
>  |     with the bottom margin of the parent block.

This still needs
s/are adjoining/collapse/

and maybe also
s/its margins/then they also/

>  | Note the above rules imply that:
>  |   * The bottom margin of an in-flow block element with a
>  |     'height' of 'auto' collapses with its last in-flow block-level
>  |     child's bottom margin if the element has no bottom padding and
>  |     no bottom border and the child's bottom margin does not collapse
>  |     with a top margin that has clearance.

Whilst recognizing that this is non-normative text, there's no such
thing as "a top margin that has clearance", so I suggest:

   "and the child's bottom margin does not collapse with the top margin
    of an element (possibly itself) that has clearance."

(The idea in 9.5.2 that clearance is introduced above the top margin of
a clearing element is not fully correct, as I demonstrated at the very
end of [1]. Rather, it's introduced above the collapsed margin resulting
from collapsing the top margin with subsequent margins, in the case that
such a collapsed margin exists.)

[1] http://lists.w3.org/Archives/Public/www-style/2010Aug/0259.html

Anton Prowse
Received on Friday, 20 August 2010 18:30:25 UTC

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